The subject matter disclosed herein relates generally to the use of semiconductor-based radiation detectors.
Non-invasive imaging technologies allow images of the internal structures or features of a subject (patient, manufactured good, baggage, package, or passenger) to be obtained non-invasively. In particular, such non-invasive imaging technologies rely on various physical principles, such as the differential transmission of X-rays through the target volume or the reflection of acoustic waves, to acquire data and to construct images or otherwise represent the internal features of the subject.
For example, in X-ray-based imaging technologies, X-ray radiation spans a subject of interest, such as a human patient, and a portion of the radiation impacts a detector where the intensity data is collected. In digital X-ray systems, a detector produces signals representative of the amount or intensity of radiation impacting discrete pixel regions of a detector surface. The signals may then be processed to generate an image that may be displayed for review.
In one such X-ray-based technique, known as computed tomography (CT), a scanner may project fan-shaped or cone-shaped X-ray beams from an X-ray source at numerous view angle positions about an object being imaged, such as a patient. The X-ray beams are attenuated as they traverse the object and are detected by a set of detector elements which produce signals representing the intensity of the incident X-ray intensity on the detector. The signals are processed to produce data representing the line integrals of the linear attenuation coefficients of the object along the X-ray paths. These signals are typically called “projection data” or just “projections”. By using reconstruction techniques, such as filtered backprojection, images may be generated that represent a volume or a volumetric rendering of a region of interest of the patient or imaged object. In a medical context, pathologies or other structures of interest may then be located or identified from the reconstructed images or rendered volume.
Radiation detectors used in these types of imaging techniques may operate in an energy-integrating mode (i.e., readout of the total integrated energy deposited during an acquisition interval) or a photon-counting mode (each individual X-ray photon is detected and counted). Energy integration is the conventional mode for X-ray detectors in most clinical applications. However, photon-counting detectors offer other benefits relative to energy-integrating detectors, such as improved resolution, the ability to improve contrast-to-noise ratio by optimally weighting detected photons, the ability to better delineate materials in the X-ray beam, and so on. Photon-counting detectors may also, depending on their implementation, provide energy-discriminating functionality, such that each photon detected may be characterized or “binned” based on its observed energy.
Radiation detectors typically operate based on two different physical principles. Certain detectors employ a scintillating intermediary which, in response to X-ray events emits optical photons at the location of the X-ray event. The optical photons may then be detected and localized using known photodetection techniques. Alternatively, a detector may employ direct-conversion of incident X-rays to electrical signals, such as a detector based on silicon strips or other semiconductor materials (such as cadmium zinc telluride (CZT) or cadmium telluride (CdTe)) that generate a measurable signal when the semiconductor substrate is itself exposed to X-ray photons. One issue that can arise in such direct-conversion contexts, however, is the charge cloud associated with a conversion event may span multiple detector pixels, which can lead to erroneous measurements.